Muffling block

ABSTRACT

Sound-absorbing blocks of box-like shape are combined to form a unit. The unit consists of two kinds of blocks, one being shorter and having a lower density than the other. In use, every unit is fixed to a wall or ceiling so that a discontinuous side of each unit faces away from the surface of the wall or ceiling and a smooth side thereof is fixed to the latter. Every unit consists of four or five sound-absorbing blocks which latter are made of a fiber material. One of the features of this invention is that the unit can be adapted for use in a rather wide sound-absorbing chamber by making the walls thin. Another feature is that the structure of the sound-absorbing unit is so simple that the manufacturing cost is very low.

[451 Jan. 22, 1974 MUFFLING BLOCK [75] Inventor:

[73] Assignee: KabushikiKaisha FujiiKogyo, Tokyo, Japan [22] Filed: Dec.15, 1972 [21] Appl. No.: 315,483

Shozo Fujii, Tokyo, Japan [30] Foreign Application Priority Data Sept.6, 1972 Japan 47-103249 [52] U.S. Cl. 181/33 G, 181/33 GD [58]FieldofSearch l81/63,71,33 GB,

181/33 GD. 33 G, 30, 33 GE; 52/144 [56] References Cited UNITED STATESPATENTS 1,875,074 8/1932 Mason 181/33 G UX 1,976,282 10/1934 lzumiyama181/33 G UX 2,200,650 5/1940 Welch 52/144 1,878,409 9/1932 Lyford 52/1441,790,938 2/1931 Marcus 52/144 2,549,189 4/1951 Gabo 181/33 G PrimaryExaminer-Stephen J. Tomsky Assistant Examiner-John F. Gonzales Attorney,Agent, or Firm-Michael S. Striker 5 7] ABSTRACT Sound-absorbing blocksof box-like shape are combined to form a unit. The unit consists of twokinds of blocks, one being shorter and having a lower density than theother. In use, every unit is fixed to a wall or ceiling so that adiscontinuous side of each unit faces away from the surface of the wallor ceiling and a smooth side thereof. 18 fixed to the latter. Everyuriit consists of four or five sound-absorbing blocks which 10 Claims,10 Drawing Figures PATENTED JAN 2 2 I974 sum 1 or 3 F ig.2b

F ig.2a

PRIOR ART d dd dd PATENTED JAN 2 2 I974 sum 2 OF 3 .1 R A m R P PRIORART PRIOR ART PAT JAN I I ENIED 22574 ($786,898

sum 3 [1F 53 I MUFFLING BLOCK BACKGROUND OF THE INVENTION This inventionrelates to a unit for absorbing sound, especially to a unit composed ofblocks and capable of absorbing low-pitch sound effectively, and whichis of simple construction.

A known block for use in this type of unit is shown in FIG. 4a. Theblock is shaped like a wedge at one end and is arranged together withseveral similar blocks in a mosaic pattern, the assembled blocks beingsecured to a frame before use. However, because of the taper of theblocks and of the difficulty in securing them to the frame, which isnecessary for protecting the tapered blocks, the manufacturing costbecomes expensive. An arrangement of the blocks of FIG. 4a is shown inFIG. 5.

Another disadvantage of this type of block resides in the fact that theeffective area of a sound-absorbing chamber utilizing such blocks isgreatly reduced due to the excessive space required by the blocks whenthe sound-absorbing effect of the chamber is to be increased. FIG. 4bshows the results of experiments in which the relation between thelength T of the wedgeshaped portion of such blocks and the frequency(Hz) of the sound absorbed was determined. The curve in this Figure,which was obtained for 98 percent soundabsorption, is seen to be linearand is inclined at an angle of 45 to the vertical. The data in thisFigure is applicable where the width (B) of the wedge-shaped portion atits widest point is between and 30 cm. and where the density of theglass fibers of which the blocks are composed is between and 64 kg/m. Itwill be clear that, in order to absorb 98 percent of sound having afrequency of 150 Hz, the length (T) of the wedgeshaped portion should be60 cm., whereas if the sound has a frequency of 100 Hz, the length (T)should be 85 cm. For the purpose of absorbing lower pitched or lowerfrequency sound, the length of the wedge portion (T) should be longerand the thickness of the absorbing wall or the depth of the block shouldalso be increased.

Another known construction, proposed by the instant applicant, is shownin FIG. 2a. The unit (3') shown in this Figure is composed of glassfiber, soundabsorbing blocks (1) and (2') having the same width anddensity but being of different lengths, the blocks (1') being longerthan the blocks (2'). The blocks (1') and (2) are alternately arrangedand are secured to a non-illustrated frame. Although the manufacturingcosts for this known construction is low, it is not possible to obtainperfect sound-absorption. This is shown by curve a in FIG. 3 whichindicates that 98 percent sound-absorption is obtained only atfrequencies of 120 Hz or so whereas at frequencies of about 200 Hz, thepercentage of sound-absorption becomes very low.

It has been found that wedge-shaped blocks are effective in absorbinglow-pitched sound. However, as mentioned above, such blocks have thedisadvantage that the effective area of a sound-absorbing chamberwherein they are utilized is greatly reduced.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a unit comprising sound-absorbing blocks which is effective forabsorbing low-pitched sound and which includes a plurality of two typesof sound-absorbing blocks, one of which is made from glass fibers, andwherein the two types of blocks have different densities and lengths andare combined with each other.

Another object of the present invention is to provide a unit comprisingsound-absorbing blocks which is effective for absorbing low-pitchedsound and which does not require a large decrease in the effective areaof a sound-absorbing chamber in which it is utilized in order to beeffective.

These and further features and advantages of the invention will best beunderstood from the following detailed description of an exemplaryembodiment thereof taken in conjunction with the accompanying drawingswherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a unitof alternately arranged longer and shorter sound-absorbing blocks inaccordance with the invention.

FIG. 2a is a side view of known sound-absorbing blocks fixed together.

FIG. 2b is a side view of one embodiment according to the inventionshowing the relationship between the lengths of the longer and shorterblocks.

FIG. 2c is a view similar to FIG. 2b but showing another embodiment ofthe present invention.

FIG. 3 is a diagram showing the percentage soundabsorption for theembodiments of FIGS. 2a, 2b and 2c.

FIG. 4a is a perspective view of a known soundabsorbing block.

FIG. 4b is a graph showing the relationship, at 98 percentsound-absorption, between the length of the wedge-shaped portion of theblock of FIG. 4a and the frequency of the sound absorbed.

FIG. 5 is a perspective view showing a unit composed of the blocks ofFIG. 4a.

FIG. 6a is a perspective view showing one arrangement of units ofsound-absorbing blocks according to the invention mounted on a wallframe.

FIG. 6b is a view similar to FIG. 6a but showing a differentarrangement.

DETAILED DESCRIPTION OF THE INVENTION In the drawing, the numeral 1denotes soundabsorbing blocks made of a material such as glass fibersand having a highdensity (d). The numeral 2 denotes sound-absorbingblocks made of glass fibers and having a low density (d). The blocks 1and 2 have the shape of an oblong, flat box. The blocks 1 are of greaterwidth than the blocks 2 although the blocks 1 and 2 have the samethickness.

A unit 3 comprises a plurality of blocks 1 and 2, as shown in FIGS. 1,2b and 2c,-which are fixed relative to one another by a suitable frameor by adhesive means. The blocks 1 and 2 are arranged alternately sothat a wider block is always located adjacent a narrower block.

Every unit 3 has smooth or continuous faces and discontinuous faces. Theunits 3 are secured to the surface of a wall or ceiling with acontinuous face abutting this surface and with a discontinuous facelocated outwardly thereof. This is illustrated in FIGS. 6a and 6b wherea plurality of units 3 are shown secured to a wall frame or support 4 orthe like. It will be seen that adjacent ones of the units 3 are rotatedrelative to one another by 90. The assembly of the units 3 may beextended in any of the directions indicated by the arrows simply byadding additional ones of the units 3.

The behavior of the sound-absorbing blocks of the present invention willnow be explained on the basis of the above-described structure.

It is assumed that the characteristics of the blocks of FIGS. 2b and 2care as follows:

FIG. 2b FIG. 2c a=Density of a wider block 24 kgJM 24 kgJM l=Thicknessof each wider block l mm. 100 mm. Width of a wider block 2L--'400 mm.2.5L=500 mm. d'=Density of a nag r oyv e r blg r :k 48kg./M 32 l g./M l=Thickness of each narrower block lOO mm. 100 mm. Width of a narrower mI block L =200 mm. L =200 mm.

The curves b and c in FIG. 3 correspond, respectively, to FIGS. 2b and20. It is seen that 98 percent sound absorption may be obtained atfrequencies as low as 140 and 100 Hz for the respective structures ofFIGS. 2b and 20. This means that, in the case of FIG. 2c, thelow-pitched sound to be absorbed by 98 percent may have a frequency aslow as 100 Hz. The experimental data of FIG. 3 show that, by suitablycombining wider and narrower blocks having different densities, mostsound from the high-frequency to the lowfrequency range can beeffectively absorbed.

According to the present invention, by varying the densities and lengthsof the blocks, it becomes possible to absorb the sound in asound-absorbing chamber as desired. In particular, it has becomepossible to absorb low-pitched sound even though the sound-absorbingwalls of the chamber are thin so that the effective area of the chamberis not greatly reduced, whereas it has been thought impossibleheretofore to absorb lowpitched sound without significantly reducing theeffective area of the sound-absorbing chamber. Thus, the invention has aremarkable sound-absorbing effect.

While the principles of the invention have now been made clear byillustrative embodiments, it will be obvious to those skilled in the artthat many modifications in structure, arrangement, proportions,elements, materials and components used in the practice of theinvention, which are particularly adapted for specific environments andoperating requirements, may readily be made therein without departingfrom these principles.

The appended claims are therefore intended to cover and embrace any suchmodifications, within the limits only of the true spirit of theinvention.

from said first density, said first and second blocks being arrangedwith said edge faces located in a common plane, and said unit beingmountable on a wall, ceiling or the like.

2. A sound-absorbing unit as defined in claim 1, further comprisingadditional ones of said first and second blocks; and wherein each ofsaid first blocks is in contact with said second blocks only, and eachof said second blocks is in contact with said first blocks only.

3. A sound-absorbing unit as defined in claim 2, wherein said unitcomprises two of said first blocks and two of said second blocks.

4. A sound-absorbing unit as defined in claim 2, wherein said unitcomprises two of said first blocks and three of said second blocks.

5. A sound-absorbing unit as defined in claim 2, wherein said unitcomprises three of said first blocks and two of said second blocks.

6. A sound-absorbing unit as defined in claim 1, said first and secondblocks each having a length, a width and a thickness; and wherein saidfirst and second dimensions correspond to the respective widths of saidfirst and second blocks, the length of said first block beingsubstantially equal to the length of said second block, and thethickness of said first block being substantially equal to the thicknessof said second block.

7. A sound-absorbing unit as defined in claim 1, further comprising aframe; and wherein said first and second blocks are mounted on saidframe thereby being connected with one another.

8. A sound-absorbing unit as defined in claim 1, wherein said first andsecond blocks comprise glass fibers.

9. A second absorbing unit as defined in claim 1, wherein said firstdimension is substantially equal to twice said second dimension.

10. A sound-absorbing unit as defined in claim 1, wherein said firstdimension is substantially equal to two and one-half times said seconddimension.

1. A sound-absorbing unit, comprising at least one first block ofsubstantially rectangular cross section having an edge face and a firstdimension in a direction normal thereto, said first block having a firstdensity; and at least one second block of substantially rectangularcross section connected with said first block in surface-to-surfacecontact, said second block having an edge face and a second dimension ina direction normal thereto which is smaller than said first dimension,and said second block having a second density different from said firstdensity, said first and second blocks being arranged with said edgefaces located in a common plane, and said unit being mountable on awall, ceiling or the like.
 2. A sound-absorbing unit as defined in claim1, further comprising additional ones of said first and second blocks;and wherein each of said first blocks is in contact with said secondblocks only, and each of said second blocks is in contact with saidfirst blocks only.
 3. A sound-absorbing unit as defined in claim 2,wherein said unit comprises two of said first blocks and two of saidsecond blocks.
 4. A sound-absorbing unit as defined in claim 2, whereinsaid unit comprises two of said first blocks and three of said secondblOcks.
 5. A sound-absorbing unit as defined in claim 2, wherein saidunit comprises three of said first blocks and two of said second blocks.6. A sound-absorbing unit as defined in claim 1, said first and secondblocks each having a length, a width and a thickness; and wherein saidfirst and second dimensions correspond to the respective widths of saidfirst and second blocks, the length of said first block beingsubstantially equal to the length of said second block, and thethickness of said first block being substantially equal to the thicknessof said second block.
 7. A sound-absorbing unit as defined in claim 1,further comprising a frame; and wherein said first and second blocks aremounted on said frame thereby being connected with one another.
 8. Asound-absorbing unit as defined in claim 1, wherein said first andsecond blocks comprise glass fibers.
 9. A second absorbing unit asdefined in claim 1, wherein said first dimension is substantially equalto twice said second dimension.
 10. A sound-absorbing unit as defined inclaim 1, wherein said first dimension is substantially equal to two andone-half times said second dimension.